Project Summary/Abstract Across the US, substance use (SU) is a significant public health concern. Rates of opioid use disorders have increased exponentially, with 60% of overdoses attributed to heroin and illicit synthetics. Although opioid use among youth is low compared to adults, experimentation and regular use increases later in adolescence as youth transition to adulthood. Juvenile justice (JJ)-involved youth represent a particularly vulnerable population, as they often experience mental health disorders, dysfunctional family/social relationships, and complex trauma, placing them at greater risk for SU and substance use disorders (SUDs). To ensure that these youth do not become another opioid statistic, innovative and effective prevention interventions are needed. We propose to adapt and test an intervention for preventing initiation and/or escalation of opioid misuse among older JJ-involved adolescents. The target enrollment group will be youth aging out of JJ (16-18 years) who are transitioning to their communities after a period of detainment in a secure treatment or correctional facility. Trust-based Relational Intervention (TBRI; a relational, attachment-based intervention that promotes emotional regulation through interaction with responsive adults) will be adapted as a prevention intervention targeting youth at risk for SU (especially non-medical use of opioids). Safe adults (e.g., parent/guardian) will be trained in behavior management techniques for empowering youth to appropriately express their needs, connecting them with others in pro-social ways, and correcting or reshaping undesirable behavior. The proposed Effectiveness/Implementation study will be conducted in 3 phases. Phase 1 will adapt elements of TBRI for JJ youth, develop intervention manuals and study protocols, examine the acceptability of the adapted intervention, and test the feasibility of the proposed study protocol (e.g., agency and youth recruitment). Feedback from 15 youth/safe adult dyads will be solicited as part of this phase. Phase 2 will examine both the effectiveness of TBRI for preventing opioid misuse and the comparative utility of three support formats: (1) TBRI Training only, (2) TBRI Training + Structured Coaching, or (3) TBRI Training + Responsive Coaching (triggered by the youth?s need/risk). A total of 360 youth/safe adult dyads will be recruited from 6 participating JJ facilities over a 3-year period, and followed for 18 months post-release (20 youth-adult dyads/year per facility). This design enables a comparison of TBRI versus SRP (using a stepped-wedge design where each facility serves as its own control) plus a randomized control trial comparing 3 TBRI support formats. Phase 3 will examine barriers and facilitators of TBRI sustainment. Sixty JJ staff (10 from each agency) will provide input annually via focus groups and surveys. TCU will work with administrators and staff at each JJ facility to implement a sustainment plan, which will include developing in-house TBRI expertise (i.e., staff training and implementation assistance). Successful completion of study aims will provide a test of the adapted intervention and will facilitate sustainment by providing training and implementation support to participating facilities.